1. Field of the Invention
The field of the present invention relates generally to cylinder valve opening mechanisms and, in particular, to cylinder valve opening mechanisms for use in internal combustion engines. More particularly, the present invention relates to cam lobe operated devices which hydraulically control cylinder valves in internal combustion engines to obtain improved operating characteristics, including increased horsepower, reduced fuel consumption and/or improved emissions quality.
2. Background
Internal combustion engines have been and continue to be used in virtually every mode of transportation and for all types of power supply needs throughout the entire world. These engines have been the subject of intensive efforts in the United States and most industrialized countries throughout this century to improve their operating characteristics. Certain of these efforts have been addressed to improving the horsepower, fuel consumption and/or exhaust air quality of these engines. However, until recently, very little advancement has been made in the basic mechanism for operating the cylinder intake and exhaust valves.
The typical internal combustion engine comprises a series of cylinders having pistons and valves. Air and fuel are combined in the piston chamber and ignited by a spark from a spark plug. The fuel and air are fed into the piston chamber through an intake valve and, after combustion, exhaust air is forced out through the exhaust valve. To obtain proper performance of the fuel/air igniting sequence, the valve activating mechanism must open and close the intake and exhaust valves at the proper times. Due to relatively high engine operating speeds, this process happens at a very fast rate.
The valve activating mechanism consists, primarily, of the camshaft, valve lifter, push rod and rocker arm. The valve activation mechanism is driven by the camshaft, which has a series of cams having a cam lobe and cam heel. One end of the valve lifter contacts the cam lobe when the cam rotates under it. The opposite end of the valve lifter contacts the push rod, which contacts one side of the rocker arm. The other side of the rocker arm contacts the valve stem to open and close the valve. As the cam lobe rotates under the lifter, the push rod pushes up one end of the rocker arm, causing it to pivot and push down the valve at the opposite end of the rocker arm, thereby unseating and opening the valve. The rate of valve lift, amount of valve lift and the duration of that lift are commonly referred to as the "valve event." A valve spring below the valve side of the rocker arm encircles the valve stem and applies an upward force to close the valve, along with combustion pressure from inside the piston chamber. The upward force exerted by the push rod must be sufficient to overcome the valve spring force.
The conventional cylinder valve activation mechanism can provide optimum intake and exhaust valve timing over only a limited range of engine speed, measured in revolutions per minute ("RPMs"). Typically, the optimum operation of these valves is set to occur at or near engine speeds that occur at the engine's rated horsepower. At this speed, high volumetric efficiency is achieved by closing the exhaust valve late and opening the intake valve early (referred to as "valve overlap"). Unfortunately, valve settings that provide valve overlap are not well suited to low engine speeds and, as a result, dramatically reduce the volumetric efficiency of the engine. For improved efficiency and to obtain optimum performance at low engine speeds, the valves need to open when the piston is at or near the top or bottom of its cycle.
One way to improve performance for the typical internal combustion engine at low engine speeds is to increase the amount of time the valve lifter does not contact the cam (i.e., increasing the crankshaft rotating degrees relative to the opening of the valves--referred to as "valve lash"). Increasing valve lash shortens the amount of time the valve is open and reduces overlap. Although this improves the operation of the engine at low speeds, excessive valve lash results in undesirable noise, wear and loss of horsepower at higher engine speeds.
3. Related Art
A number of related art devices address the limitations of the mechanical valve activation mechanism of the conventional internal combustion engine. Such devices include U.S. Pat. No. 4,656,976 to Rhoads, U.S. Pat. No. 5,193,494 to Sono, U.S. Pat. No. 5,193,495 to Wood, U.S. Pat. No. 5,195,474 to Urata, U.S. Pat. No. 5,231,959 to Smietana, U.S. Pat. No. 5,673,658 to Allmendinger and U.S. Pat. No. 5,682,846 to Scharnweber. None of these related art devices solve the problems with conventional valve activation mechanisms identified above in the manner solved by the present invention.
Each of the aforementioned patents present devices and mechanisms for internal combustion engines that require significant modification to the typical internal combustion engine or which are otherwise not suitable for obtaining the benefits sought by those in the field. As such, despite the potential benefits to be obtained by improving the valve activation mechanism, the inventions set forth in the aforementioned patents, or derivations thereof, are generally not utilized in present day internal combustion engines. Consequently, a need exists for a hydraulically operated variable valve control mechanism that is compatible with and relatively easy to install in the typical internal combustion engine.